Cleanup "Reporting an issue" section

[skirpichev]

Now this lists only few examples from actually available options.

Closes #1403

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📚 Documentation preview 📚: https://cpython-devguide--1407.org.readthedocs.build/

[Mariatta]

I think we should still list all the available choices instead of only a sampling.
Though I'm ok with removing the last two (getting help/proposing new features)

[JelleZijlstra]

I feel the full list is likely to go out of date as we change the issue template, and duplicating it here isn't very useful as users can see the same information by going to https://github.com/python/cpython/issues/new/choose.

[skirpichev]

I think we should still list all the available choices instead of only a sampling.
Though I'm ok with removing the last two (getting help/proposing new features)

I think that 1st sentence contradicts to the 2nd.

I feel the full list is likely to go out of date as we change the issue template

This increase maintenance burden for no real benefits. Why do we want here list all (well, not all actually even with @Mariatta suggestion;)) currently available options? They seems to be just examples and not referenced somehow in following text.

[willingc]

@skirpichev Some of this text is left over from before we moved the issues to GitHub.

Here's the existing list @JelleZijlstra's link:

Since this section of the guide is aimed at new/future contributors, I think it is essential to add back the wording on privately reporting security vulnerabilities.

[willingc]

Thanks @skirpichev.